In recent years, to meet requirements for downsizing, weight saving and high performance of electronic equipments, downsizing, reduction in thickness and reduction in pitch of semiconductor packages are rapidly in progress. Further, the mounting method tends to be mainly surface mounting whereby high density mounting is easy. Under such circumstances, high performance is required also for a sealing material for semiconductors (hereinafter referred to as a “sealing material”), and it is required to further improve the soldering heat resistance, moisture resistance, low thermal expansion and electrical insulating properties. In order to satisfy such requirements, methods have been proposed such that the variation coefficient of the particle size distribution of a silica powder is made to be at most 10% to make the particle size distribution sharp (Patent Document 1), the sphericity of particles having a particle size of at least 45 μm is made to be from 0.75 to 1.0 thereby to increase the sphericity in the coarse powder region (Patent Document 2), and a spherical fine silica powder having an average particle size of from about 0.1 to 1 μm is added in a small amount (Patent Document 3), and it has been attempted to improve the flowability and packing properties of the sealing material. However, such properties have been improved so much that there has been a problem of formation of a flash, such that a sealing material is likely to flow out from an air bent portion of a mold during molding.
Patent Document 1: JP-A-11-124504
Patent Document 2: JP-A-2004-123849
Patent Document 3: JP-A-5-239321